The invention relates to a sensor membrane and to a process for the preparation thereof.
Thus, amongst others, EP 0 585 212 A2, for example, describes the sensor membrane of an optical sensor with which O2, H2O2, SO2 or halogenated hydrocarbons can be detected in a sample. Here, an indicator substance has been incorporated into an appropriate polymer matrix, which indicator substance changes its optical properties as a result of the presence of said analytes. Thus, for example, the known luminescence quenching, i.e. a change in the luminescence intensity which arises as a result of contact of the analytes suitable therefor with the corresponding indicator, can be exploited and, accordingly, the respective analyte concentration can be measured. However, a change in the luminescence fading time or the optical absorption of light waves are also suitable evaluatable parameters.
The prior art discloses various polymers which are more or less suitable for the preparation of a sensor membrane. These polymers are subject to a number of basic prerequisites. These are at least a certain degree of permeability for the respective analytes, a possibility of incorporating the indicator into the polymer matrix without the latter losing its function, and transparency for the wavelength ranges of the measurement light which are used.
The polymers described hitherto for the preparation of a sensor membrane for determining, for example, oxygen are, for example, cellulose, polystyrenes, polytetrahydrofuran and derivatives thereof (EP 0 585 212 A2), PVC (U.S. Pat. No. 4,003,707) and PVC containing plasticizer (U.S. Pat. No. 4,752,115), partially fluorinated polyurethanes (WO 95 08 107, WO 93 18 391, U.S. Pat. No. 5,453,248), silicones in various modifications (U.S. Pat. No. 4,003,707, U.S. Pat. No. 5,0303,420, WO 95 22 759, WO 94 04 241, WO 96 37 768) in which the indicator is reportedly present in dissolved form. By contrast, polymers to which the indicator has been coupled by a chemical bond (U.S. Pat. No. 5,580,527) or else the indicator has been absorbed to a particle of, for example, silicon dioxide, which has then been incorporated into a polymer matrix (U.S. Pat. No. 4,003,707) are also described. A sensor membrane based on a ceramic as matrix material has also been described (U.S. Pat. No. 5,490,490).
However, polymers described and used hitherto do not have further properties essential for many applications. This refers essentially to their relatively low mechanical and thermal stability, in which case it is to be noted that for many applications a single or repeated sterilization, e.g. with water vapor, may be required. However, the high temperatures which arise during this process lead in the case of the known materials to undesired changes in their physicochemical and optical properties, rendering them unsuitable for such applications.
A further disadvantage arises from the poor fixing of the sensitive indicator, e.g. the transition metal complexes, in the polymer matrices used. Said complexes are poorly soluble in hydrophobic, relatively soft gas permeable silicone membranes, for which reason they have to be adsorbed to filler materials. The heterogeneous distribution of additionally light-scattering particles has optical disadvantages. The transition metal complexes can be washed out of polyanionic materials relatively easily since they exhibit ion exchanger behavior and are hydrophilic. Moreover, the latter materials have the disadvantage that they can be penetrated by the mostly aqueous sample solution, resulting in poor chemoselectivity to the substances dissolved in the aqueous sample solution to which the indicator exhibits cross sensitivity. Furthermore, the analyte-indicated changes in the transition metal complexes in an ionic environment are often irreversible, for which reason use in a reversibly operating sensor is not possible.
This object preferably is achieved according to the invention. Advantageous embodiments and developments of the invention will be apparent from the description of the invention provided herein.